1. Field of the Invention
The present invention relates to a lighting system for a vehicle such as a car, and more particularly to a lighting system for a vehicle comprising lamp deflection angle control means for follow-up changing an irradiating direction of a light of a lamp corresponding to a running situation, for example, an adaptive front-lighting system (hereinafter referred to as an AFS) which can implement an enhancement in precision in deflection angle control.
2. Description of the Related Art
The AFS proposed to enhance the running safety of a car detects information about the steering angle of a steering wheel SW of the car, the speed of the car, and the running situation of the car by means of a sensor 1 and sends the detected output to an electronic control unit (hereinafter referred to as an ECU) 2 as shown in a conceptual view of FIG. 1. The ECU 2 controls swivel type lighting units (lamps) 3R and 3L provided on the right and left of the front part of the car, that is, a headlamp 3 capable of deflecting and controlling an irradiating direction in a lateral direction based on the output of the sensor which is input. The swivel type lighting units 3R and 3L have such a structure that a reflector provided in the headlamp can be rotated in a horizontal direction and is driven to be rotated by a driving force source such as a motor, for example. A mechanism for a rotation will be referred to as an actuator. According to the AFS of this type, when the car runs on a curved road, it is possible to illuminate the curved road corresponding to the running speed of the car. Thus, the AFS is effective for enhancing a running safety.
In order to implement a proper illumination in the AFS, however, it is necessary to cause the steering angle of a steering wheel to correctly correspond to the deflection angle of a swivel type lighting unit. When the correspondence cannot be taken, the optical axis of the swivel type lighting unit cannot illuminate a region in a direction which is not preferable for the running direction of the car, for example, a forward part in the straight running or curving in an opposite direction which is carried out by the car. Alternatively, a car running in an opposite direction is dazzled due to a deflection toward the opposite lane side. Thus, there is a problem of the running safety In a conventional AFS, therefore, an actuator of a swivel type lighting unit is provided with a detector for detecting a deflection angle. For example, a potentiometer is provided in a part of a gear mechanism for deflecting the swivel type lighting unit and a deflection angle is detected from the output of the potentiometer. However, the provision of the detector is not preferable because the structure of the actuator is complicated and large-sized. For this reason, it is proposed that the rotating angle of a motor to be a driving source of the actuator is detected and the deflection angle of the swivel type lighting unit is thus detected. A hole IC for outputting the number of pulses corresponding to the amount of the rotation of the motor is used for the rotation detector. However, the rotation detector of this type can detect the amount of the rotation (the rotating angle) in such a state that the motor is operated continuously. When a power supply is once turned OFF, the output of the rotation detector is reset. For this reason, the deflection angle of the swivel type lighting unit cannot be detected when the power supply is turned ON again. Consequently, there is a problem in that the running safety cannot be obtained and a car running in an opposite direction is dazzled as described above.
In the conventional AFS, moreover, a deflecting operation is always carried out irrespective of the lighting state of the lighting unit. For this reason, also in the case in which the lighting unit is turned OFF, it is swiveled in conformity to the steering angle of a steering wheel. The swiveling operation of the lighting unit is wasteful during power-off. The wasteful swiveling operation causes a damage due to the fatigue of the actuator, resulting in a deterioration in the lifetime and reliability of a device.